As I told you above, the declaration of war was handed over to an Austrian major for transmission to Count Stancowick, the Austrian governor of Mantua, on the evening of the 19th, by Colonel Bariola, sous-chef of the general staff, who was accompanied by the Duke Luigi of Sant' Arpino, the husband of the amiable widow of Lord Burghersh. The duke is the eldest son of Prince San Teodoro, one of the wealthiest noblemen of Naples. In spite of his high position and of his family ties, the Duke of Sant' Arpino, who is well known in London fashionable society, entered as a volunteer in the Italian army, and was appointed orderly officer to General Lamarmora. The choice of such a gentleman for the mission I am speaking of was apparently made with intention, in order to show the Austrians, that the Neapolitan nobility is as much interested in the national movement as the middle and lower classes of the Kingdom, once so fearfully misruled by the Bourbons. The Duke of Sant' Arpino is not the only Neapolitan nobleman who has enlisted in the Italian army since the war with Austria broke out. In order to show you the importance which must be given to this pronunciamiento of the Neapolitan noblemen, allow me to give you here a short list of the names of those of them who have enlisted as private soldiers in the cavalry regiments of the regular army: The Duke of Policastro; the Count of Savignano Guevara, the eldest son of the Duke of Bovino; the Duke d'Ozia d'Angri, who had emigrated in 1860, and returned to Naples six months ago; Marquis Rivadebro Serra; Marquis Pisicelli, whose family had left Naples in 1860 out of devotion to Francis II.; two Carraciolos, of the historical family from which sprung the unfortunate Neapolitan admiral of this name, whose head Lord Nelson would have done better not to have sacrificed to the cruelty of Queen Caroline; Prince Carini, the representative of an illustrious family of Sicily, a nephew of the Marquis del Vasto; and Pescara, a descendant of that great general of Charles V., to whom the proud Francis I. of France was obliged to surrender and give up his sword at the battle of Pavia. Besides these Neapolitan noblemen who have enlisted of late as privates, the Italian army now encamped on the banks of the Po and of the Mincio may boast of two Colonnas, a prince of Somma, two Barons Renzi, an Acquaviva, of the Duke of Atri, two Capece, two Princes Buttera, etc. To return to the mission of Colonel Bariola and the Duke of Sant' Arpino, I will add some details which were told me this morning by a gentleman who left Cremona yesterday evening, and who had them from a reliable source. The messenger of General Lamarmora had been directed to proceed from Cremona to the small village of Le Grazie, which, on the line of the Mincio, marks the Austrian and Italian frontier.